Method for refining polyoxymethylene dialkyl ethers by catalytic hydrogenation using a slurry bed

ABSTRACT

The present invention relates to a method for refining polyoxymethylene dialkyl ethers by catalytic hydrogenation using a slurry bed, wherein, using a slurry bed reactor of refining by hydrogenation, an equilibrium system of products containing polyoxymethylene dialkyl ethers is refined by catalytic hydrogenation, so as to remove formaldehyde contained therein. The refining method by hydrogenation described in the present invention is able to remarkably increase the extracting rate of polyoxymethylene dialkyl ethers, and the polyoxymethylene dialkyl ethers obtained after subsequent rectification have purity greater than 99.5%, yield greater than 97% and atom utilization ratio close to 100%.

TECHNICAL FIELD

The present invention relates to a method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed, whichbelongs to the field of coal-based energy chemical industry, cleanenergy and refining by chemical process.

BACKGROUND OF THE INVENTION

Recent investigation shows that, the apparent consumption of diesel fuelin China has already mounted up to 167 million tons, which leads tofrequent occurrence of short supply of diesel fuel (the domestic demandratio of diesel fuel to petrol is about 2.5:1, but the production ratiois about 2.3:1). Besides the reasons of unreasonable pricing ofdifferent types of oil products, and slow price linkage mechanism ofdomestic petroleum products with international crude oil, thefundamental reason is the restriction of resource shortage.Traditionally, diesel fuel is made from feedstock of petroleum, and theresource endowment of China characterized in relatively “rich in coal,poor in oil, and lack in gas” leads to increasingly prominentcontradiction between petroleum supply and relatively fast sustainabledevelopment of economic society. Since China became a net importer ofpetroleum in 1993, the import quantum increases fast and constantly, andthe foreign-trade dependence already surpassed 56% after 2011, which hasa severe impact on national strategic security of energy.

Furthermore, the day-by-day deterioration of crude oil quality leads tocontinuous scale expansion of domestic catalytic processing of heavy oiland increasing percentage of diesel fuel produced by catalyticprocessing, which results in gradual decrease of the cetane number (CNvalue) of diesel fuel products and significant increase of noxioussubstance discharged after combustion, therefore, the urgent problem tobe solved is to improve the CN value of diesel fuel.

The tail gas discharged by diesel engine contains a large amount ofnoxious substance such as unburned hydrocarbon compounds and particulatematter (PM), as well as CO, CO₂ and NO_(R), which are one of the mainsources of PM2.5 contamination in urban air. International Agency forResearch on Cancer (IARC) affiliated to World Health Organization (WHO)declared in June, 2012 the decision to promote the cancer hazard rankingof diesel engine tail gas, from “possibly carcinogenic” classified in1988 to “definitely carcinogenic”. As scientific research advances, nowthere is enough evidence to prove that diesel engine tail gas is one ofthe reasons that cause people to suffer from lung cancer. Furthermore,there is also limited evidence indicating that, inhaling diesel enginetail gas is relevant to suffering from bladder cancer. People come intocontact with diesel engine tail gas through various channels in dailylife and work. IARC hopes that this reclassification can providereference for national governments and other decision makers, so as toactuate them to establish more strict discharge standards of dieselengine tail gas. This significant decision undoubtedly puts forwardharsher requirements of diesel fuel quality.

Reducing the content of noxious substance such as sulfur, nitrogen andaromatic hydrocarbon in fuels by petroleum refining process such ashydrogenation is an effective technical route to improve fuel quality,but has very demanding requirements of hydrogenation catalyst andreaction process, with relatively high processing cost. Internationally,many scientific research institutes are carrying out research anddevelopment on production technologies of oxygen-containing blendingcomponents of petrol and diesel fuel, especially those diesel fuelblending components with high oxygen content and high cetane number, andthis has recently become a research hotspot in the technical field ofnew energy.

Research has indicated that, in consideration of oxygen-containingfuel's own characteristic, when coal-based or methanol-based substancewith a high oxygen content and a high cetane number is added into thefuel as a fuel additive, the discharge of hydrocarbon and CO, especiallysoot, can be effectively reduced, without changing the originalparameters of the engine or increasing the discharge of NO_(x).

So far, there is plenty of research indicating that, polyoxymethylenedimethyl ethers (abbreviated as POMDME_(n), n=2-8), which has a generalformula of CH₃(OCH₂)_(n)OCH₃ and is a yellow liquid with a high boilingpoint, an average cetane number reaching above 63 and increasingdramatically as its degree of polymerization increases, an averageoxygen content of 47%-50%, a flash point of about 65.5° C., and aboiling point of about 160-280° C., is a type of clean diesel fuelblending component with a high cetane number, and also aworld-recognized environmental friendly fuel component. Polyoxymethylenedimethyl ethers can be blended into diesel fuel, and can significantlyimprove the performance of diesel fuel without the need to modify theengine oil feeding system of the in-use vehicle. However, it isdiscovered in practical usage that, the cetane number ofpolyoxymethylene dimethyl ethers is largely influenced by its degree ofpolymerization, and polyoxymethylene dimethyl ethers with a relativelyhigh degree of polymerization is required to achieve bettereffectiveness. But, in consideration of the difficulty of polymerizationreaction in its own, relatively demanding requirements are put forwardnot only for equipment but also for process conditions, with increaseddifficulty of processing and extracting. Therefore, people graduallymove their focus onto characteristic of polyoxymethylene dialkyl ethers.Polyoxymethylene dialkyl ethers (PODE_(n)) are a series of acetalpolymers with low relative molecular weights, which compriseoxymethylene groups as main chain and low carbon alkyl groups asterminal groups, with a general formula of R(OCH₂)_(n)OR where R is analkyl chain of C_(n)H_(2n+1).

Since the terminal groups of polyoxymethylene dialkyl ethers hasrelatively high molecular weights in its own, only relatively low degreeof polymerization is required to achieve a cetane number performancesimilar to that of polyoxymethylene dimethyl ethers, and the difficultyduring the preparation process is relatively low. Polyoxymethylenedialkyl ethers have good performance of environmental protection, andwhen blended into diesel fuel at a certain percentage, they can increaseoxygen content of the oil product, and greatly reduce the discharge ofcontaminants such as SO_(x), unburned hydrocarbon compounds, PMparticulate black smoke and CO from vehicle tail gas. Becausepolyoxymethylene dialkyl ethers have a high cetane number and physicalproperty similar to that of diesel fuel, they are also a type of dieselfuel additive with very high application value.

Synthesis of polyoxymethylene dialkyl ethers (including polyoxymethylenedimethyl ethers) may be carried out by processing synthesis gas througha series of steps of methanol, formaldehyde, methylal, polyformaldehydeand dimethyl ether etc. China is a famous huge country of coal storage,and Chinese technologies of producing methanol from coal, producingmethanol from natural gas and producing methanol from coke-oven gas areincreasingly mature, and the production capacity of methanol brokethrough 50 million tons in 2012, but the rate of equipment operation ismerely about 50%, thus the problem of methanol surplus has alreadybecome very prominent, and the industrial chain of coal chemicalindustry is in an urgent need to be further extended. Therefore,developing the technology of producing polyoxymethylene dialkyl ethersfrom coal-based methanol can not only provide a new technology tosignificantly improve diesel fuel product quality, but also improve thefeedstock structure of diesel fuel production, so as to make it moresuitable for the resource endowment of domestic fossil energy andenhance the strategic security of domestic supply of liquid fuel forengines.

The preparation process of polyoxymethylene dialkyl ethers shouldcomprise three major process units, wherein, the first unit is asynthesis unit where cascade polymerization reactions and thermodynamicequilibrium reactions catalyzed by acidic catalysts take place; thesecond unit is a pretreatment unit where processing steps such asdeacidifying by neutralization and dehydration by drying take place; andthe third unit is a unit for rectification and separation of thedownstream products, and this unit attempts to separate polyoxymethylenedialkyl ethers by simple rectification or complicated rectification suchas extractive rectification, azeotropic rectification, etc.

So far, domestic and foreign research on preparation process ofpolyoxymethylene dialkyl ethers (including polyoxymethylene dimethylethers) mainly focuses on the aspects of feedstock choice, conditionoptimization and catalyst system optimization of the synthesis unit, aswell as the process technology to improve the distribution of targetproducts and increase product yield. As for optimization of feedstock ofsynthesis, there are mainly the following five techniques: the firsttechnique is synthesizing polyoxymethylene dimethyl ethers from thefeedstock of methanol, formaldehyde or aqueous formaldehyde solution orparaformaldehyde, with details described in patent literatures such asU.S. Pat. No. 6,437,195B2, US2008/0207954A1 and EP1070755A1; the secondtechnique is synthesizing polyoxymethylene dimethyl ethers from thefeedstock of methylal, trioxane or paraformaldehyde, with detailsdescribed in patent literatures such as US2007/0260094A1 and US2449469A;the third technique is synthesizing polyoxymethylene dimethyl ethersfrom the feedstock of methanol and dimethyl ether, with detailsdescribed in patent literatures such as U.S. Pat. No. 6,265,528B1; thefourth technique is developed on the basis of the foregoing threetechniques, and this technique uses alcohol-containing by-products ofother chemical processes in the prior art to synthesize mixture ofpolyoxymethylene dialkyl ethers with various degrees of polymerizationand various terminal groups, and the major representative techniques aresynthesis of polyoxymethylene dialkyl ethers with various degrees ofpolymerization and various terminal groups from the feedstock ofindustrial alcohol brewing by-products or Fischer-Tropsch synthesisby-products or C4, C5 fractions of petroleum, which are disclosed inChinese patent literatures CN102173984A and CN102180778A.

In the above-mentioned technical solutions of synthesis ofpolyoxymethylene dialkyl ethers, the separation and extraction ofsynthesized products is carried out without exception by conventionalordinary rectification, extractive rectification or azeotropicrectification of the prior art, and no further in-depth research is donein respect of the extraction unit of target products. However, it isdiscovered in practical research that, when extracting target productsby using the foregoing conventional seemingly viable means, it alwaysleads to that the extracting rate of products is not high, and thepurity of the extracted products is not satisfactory, which is notenough to meet the technical standard for blending with fossil dieselfuel and requires subsequent additional purification operations to meetthe needs, and no matter how the parameters and conditions of the entireoperating process of the extraction unit are optimized, the difficultproblem about extracting rate always cannot be solved, and nosignificant increase in extracting rate or product purity can beachieved. In practical production, in consideration of economical andvarious other aspects, no matter how great the efficiency of thesynthesis unit at the front is, the incapability of obtaining requiredproducts by effective extracting means is always a difficult problem andbottleneck that restrains the development of this technology, which isan urgent matter to be solved in this field.

SUMMARY OF THE INVENTION

The technical problem to be solved in the present invention is, byin-depth research on the process of the unit for extractingpolyoxymethylene dialkyl ethers in prior art, to find out the influencereasons of inferior extracting rate of the extraction unit and inferiorpurity of the extracted products, so as to provide a method for refiningpolyoxymethylene dialkyl ethers by catalytic hydrogenation using aslurry bed, which is able to significantly increase the extracting rateand the product purity.

To solve the above-mentioned technical problem, the present invention isachieved by the following technical solutions:

A method for refining polyoxymethylene dialkyl ethers by catalytichydrogenation using a slurry bed is provided, wherein, using a slurrybed reactor of refining by hydrogenation and in the presence ofcatalyst, an equilibrium system of products containing polyoxymethylenedialkyl ethers is refined by catalytic hydrogenation, so as to removeformaldehyde contained therein, and subsequent rectification operationsare performed on the products after formaldehyde removal.

Preferably, the catalyst is skeletal metal catalyst.

The catalyst is preferably Raney-Co, Raney-Fe, Raney-Ru, Raney-Nicatalyst, Raney-Cu catalyst or combinations thereof.

The catalyst is most preferably Raney-Ni catalyst or Raney-Cu catalyst.

Specifically, the amount of Raney-Ni catalyst used is equal to 0.2-10 wt% of the products to be refined by hydrogenation.

Preferably, the amount of Raney-Ni catalyst used is equal to 3-8 wt % ofthe products to be refined by hydrogenation.

Specifically, the amount of Raney-Cu catalyst used is equal to 0.2-10 wt% of the products to be refined by hydrogenation.

Preferably, the amount of Raney-Cu catalyst used is equal to 3-8 wt % ofthe products to be refined by hydrogenation.

Preferably, the amount of formaldehyde contained in the equilibriumsystem of products containing polyoxymethylene dialkyl ethers is 0.5-20wt %.

Preferably, the process conditions of refining by catalytichydrogenation are that: the hydrogen pressure is 1-10 Mpa, the reactiontemperature of catalytic hydrogenation is 60-150° C., and the reactiontime is 2-8 hours.

Most preferably, the process conditions of refining by catalytichydrogenation are that: the hydrogen pressure is 2-6 Mpa, the reactiontemperature of catalytic hydrogenation is 70-120° C., and the reactiontime is 3-6 hours.

Specifically, the extracting step comprises one or more operationsselected from atmospheric distillation, reduced pressure distillation,flash evaporation, rectification, phase separation and filtration.

The aforementioned technical solutions of the present invention have thefollowing advantages, as compared to the prior art:

(1) By in-depth research on the synthesis process of polyoxymethylenedialkyl ethers, the applicant has discovered that, no matter which offormaldehyde, paraformaldehyde or methylal is used as feedstock for thereaction, the entire reaction system is equilibrium and reversible, thusthe problem of incomplete reaction with low carbon alcohol (or methanol)always exists, therefore, regardless of how the reaction conditions areimproved, there is always 3.5 wt % of formaldehyde (or monomer ofdepolymerized paraformaldehyde or methylal) unable to completely reactin the product system, and the reason that leads to the difficulty ofextraction of polyoxymethylene dialkyl ether products and the lowproduct purity is mainly that the formaldehyde in the system gives riseto unexpected negative effect, that is, complexation reaction happensbetween formaldehyde and polyoxymethylene dialkyl ethers with variousdegrees of polymerization, and the products with various degrees ofpolymerization are chained together by formaldehyde to form enormouscomplexation system, which causes the entire product system unable to beextracted or refined by ordinary processes such as distillation, notonly bringing about great difficulty of separation process, but alsoseverely affecting product yield and economic efficiency; furthermore,in the rectification process oxidization and dismutation of formaldehydeinto formic acid takes place to form an acidic environment, and formicacid is a catalyst for reverse decomposition of polyoxymethylene dialkylethers, which causes the technical problem that the target products ofpolyoxymethylene dialkyl ethers are decomposed reversely and newformaldehyde is released; therefore, before extracting the targetproducts, it is necessary to specifically eliminate the small amount offormaldehyde contained in the equilibrium system, in order to releasethe respective products required and to obtain satisfactory products byother feasible means;

(2) At the same time of research on factors that influence theextraction efficiency, it is surprisingly discovered by the applicantthat, in the entire equilibrium system after synthesis of products, thewater content has a great influence on extraction efficiency and purityof the products, therefore, when choosing the process of refining byeliminating formaldehyde, it is necessary to carefully select areasonable method in order to maximally ensure the extraction efficiencyand purity of the products;

(3) In the extraction process described in the present invention, aftercareful research, the applicant has inventively discovered the keyfactors that influence the extraction efficiency of polyoxymethylenedialkyl ethers in the prior art, and has achieved high-efficiency,high-purity extraction of polyoxymethylene dialkyl ethers with variousdegrees of polymerization by specific modification of theabove-mentioned factors which have not been cared or considered by thoseskilled in the art;

(4) In the method of the present invention for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed, theunreacted formaldehyde contained in the equilibrium system of productscontaining polyoxymethylene dialkyl ethers is transformed into methanolby reduction reaction, so as to break the complicated azeotropic systembetween formaldehyde and methanol, as well as between formaldehyde andthe products, so that polyoxymethylene dialkyl ethers with puritygreater than 99.5% can be produced by atmospheric rectification and/orreduced pressure rectification of the products, and the yield ofpolyoxymethylene dialkyl ethers is greater than 97%, the atomutilization ratio is close to 100%. The technological process has nodischarge of waste water or waste residue, thus is an innovative greenprocess and technology to separate and refine polyoxymethylene dialkylethers;

(5) The method of the present invention for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed utilizes aslurry bed reactor of refining by hydrogenation together with skeletalmetal catalyst which consists of Raney-Co, Raney-Fe, Raney-Ru, Raney-Nicatalyst, Raney-Cu catalyst or combinations thereof, preferably Raney-Nicatalyst and/or Raney-Cu catalyst, to specifically and high selectivelyrefine the equilibrium products by hydrogenation of formaldehyde, so asto specifically separate and purify the products with various degrees ofpolymerization, and the aforementioned selected catalyst has highactivity and high efficiency;

(6) As for the equilibrium system after processing by the refiningmethod of the present invention, subsequent separating operations may beperformed by ordinary processing means such as atmospheric rectificationand reduced pressure rectification, and the products with variousdegrees of polymerization that have been separated have high purity andhigh yield.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to make the present invention more easily and clearlyunderstood, detailed description is further presented below, withreference of accompanying drawings, wherein,

FIG. 1 is a process flow diagram showing the method of producingpolyoxymethylene dialkyl ethers described in the present invention;

FIG. 2 is a process flow diagram showing the step of refining byhydrogenation using a slurry bed described in the present invention;

Wherein, the markings in the accompanying drawings are explained asfollows: 1-slurry bed synthesis reactor, 2-buffer tank, 3-drying tower,4-slurry bed reactor of refining by hydrogenation, 5-buffer tank,6-atmospheric rectification tower, 7-reduced pressure rectificationtower.

DETAILED DESCRIPTION OF EMBODIMENTS

As shown in FIG. 1, the process of the present invention for preparationof polyoxymethylene dialkyl ethers comprises three major process units,the first unit is a synthesis unit, and its structure includes a slurrybed synthesis reactor 1, a buffer tank 2, and a drying tower 3, wherein,the equilibrium system obtained by synthesis reaction in the slurry bedsynthesis reactor 1 is successively deacidified in the buffer tank 2 anddehydrated in the drying tower 3; the feedstock of synthesis ofpolyoxymethylene dimethyl ethers mainly consists of two parts: one partis compounds that provide low polyformaldehyde, including aqueousformaldehyde solution, trioxane, paraformaldehyde, etc., and the otherpart is compounds that provide terminal groups, including methanol,dimethyl ether, methylal, etc., and the synthesis reaction is a cascadepolymerization reaction and a thermodynamic equilibrium reactioncatalyzed by acidic catalyst; the second unit is a unit for pretreatmentand catalytic refining, and its structure includes a slurry bed reactorof refining by hydrogenation 4 and a buffer tank 5, wherein, theequilibrium system is successively processed in the slurry bed reactorof refining by hydrogenation 4 and the buffer tank 5, thereby theunreacted formaldehyde is removed; the third unit is a unit forextraction by rectification and separation, its structure includes anatmospheric rectification tower 6 and a reduced pressure rectificationtower 7, wherein, high purity polyoxymethylene dialkyl ethers arefinally obtained after the equilibrium system has passed through theatmospheric rectification tower 6 and the reduced pressure rectificationtower 7. The unreacted light components such as methylal and methanol aswell as the polyoxymethylene dialkyl ethers with boiling points lowerthan 150° C. are returned as recycle stream to the slurry bed synthesisreactor 1; the heavy components of polyoxymethylene dialkyl ethers withboiling points higher than 320° C. are also returned as recycle streamto the slurry bed synthesis reactor 1.

FIG. 2 illustrates a flow diagram of the slurry bed reactor apparatus ofrefining by hydrogenation, wherein, the products before refining (theequilibrium system) and hydrogen are mixed at a selected hydrogen-to-oilratio in a mixer and enter the slurry bed reactor (of refining byhydrogenation), and refined products of the equilibrium system areobtained after refining by hydrogenation, and subsequent extractingoperations are then performed.

In Embodiment 1 and Embodiment 2 of the present invention, as well as inComparison Example 1, the equilibrium systems of products containingpolyoxymethylene dimethyl ethers are the same, the preparation method ofwhich is that:

In a 2 L slurry bed synthesis reactor 1, 60˜80 g strongly acidiccatalyst of Amberlyst15 cation exchange resin is added, and then 1200 gin total of paraformaldehyde (or trioxane) and acetal (or methanol,ethanol, propanol, butanol, pentanol) at various molar ratios are added,wherein the molar ratios are within 1:1˜2:1. First the air in thereactor is replaced by nitrogen, then 1.5 MPa of initial nitrogen isfilled in, the reaction mixture is heated up to the reaction temperatureof 70-130° C. and reacts under stirring for 0.5˜6 hours, thereby theequilibrium system of products containing polyoxymethylene dimethylethers are obtained, wherein the product distribution and yield of thetarget product POMDME_(n) are shown in Table 1.

TABLE 1 product distribution and yield of the target product POMDME_(n)of the equilibrium system of products containing polyoxymethylenedimethyl ethers Products Boiling Point/° C. Content/wt. % Formaldehyde−19.5  3.0~10.0 Methanol 64.7 2.0~5.0 Methylal 42.3 28.0~30.0 POMDME₂105 25.0~26.0 POMDME₃ 156 10.0~13.0 POMDME₄ 202 5.0~6.0 POMDME₅ 2423.0~3.5 POMDME₆ 280 2.0~2.5 POMDME₇ 313 0.5~1.0 POMDME₈ 320 0.2-0.5ΣPOMDME₂₋₈ wt % ~50.0

Embodiment 1

First, 63 g Raney-Ni catalyst is loaded into a 2 L pressurized slurrybed reactor of refining by hydrogenation 4;

Then, an equilibrium system of 1260 g products containingpolyoxymethylene dimethyl ethers is refined by catalytic hydrogenation,the amount of Raney-Ni catalyst used is equal to 5 wt % of the overallreaction products to be refined, and the process conditions are: thehydrogen pressure is 6 Mpa, the reaction temperature of refining by theslurry bed (i.e. the reaction temperature of catalytic hydrogenation) is70° C., and the reaction time is 4 hours;

Finally, the formaldehyde contained is hydrogenated into methanol by thecatalytic function of Raney-Ni, and the methanol generated constitutes acomponent of the equilibrium products, thereby no other foreigncomponent is generated while removing formaldehyde. The constituents anddistribution of the main products before and after refining by catalytichydrogenation are shown in Table 2.

The equilibrium system after refining by catalytic hydrogenation isextracted, and the extraction process utilizes the atmosphericrectification technology, with tower plate number of 10˜40, gastemperature of 48˜58.0° C. at tower top, temperature of 100˜120° C. attower bottom, feedstock temperature of 60˜90° C., and reflux ratio of1.0˜3.0. After the extraction is finished, the testing result ofextraction rate of the products is shown in Table 3.

Embodiment 2

First, 37.8 g Raney-Cu catalyst is loaded into a 2 L pressurized slurrybed reactor of refining by hydrogenation;

Then, an equilibrium system of 1260 g products containingpolyoxymethylene dimethyl ethers is refined by catalytic hydrogenation,the amount of Raney-Cu catalyst used is equal to 3 wt % of the overallreaction products to be refined, and the process conditions are: thehydrogen pressure is 2 Mpa, the reaction temperature of refining by theslurry bed (i.e. the reaction temperature of catalytic hydrogenation) is110° C., and the reaction time is 4.5 hours;

Finally, the formaldehyde contained is hydrogenated into methanol by thecatalytic function of Raney-Cu, and the methanol generated constitutes acomponent of the equilibrium products, thereby no other foreigncomponent is generated while removing formaldehyde. The constituents anddistribution of the main products before and after refining by catalytichydrogenation are shown in Table 2.

This embodiment utilizes the same extraction process as in Embodiment 1to perform the extraction operations.

In Embodiment 1 and Embodiment 2, the constituents and distribution ofthe main products before and after refining by catalytic hydrogenationare shown in Table 2 (Note: the symbol “˜” therein means being closeto).

TABLE 2 constituents and distribution of the main products before andafter refining by hydrogenation catalyzed by Raney-Cu catalyst (orRaney-Ni catalyst) Constituents Conversion Methanol FormaldehydeMethylal ΣPODE₂₋₈ ΣPODE_(n>8) rate of Selectivity System wt % wt % wt %wt % wt % formaldehyde/% of catalyst/% Before refining 3.7 7.8 34.0 54.00.5 — — by hydrogenation After refining 11.5 0.01 34.0 54.0 0.5 ~100~100 by hydrogenation in Embodiment 1 After refining 11.48 0.02 34.553.5 0.5 ~99.7 ~100 by hydrogenation in Embodiment 2

Thus it can be seen that, the catalyst used in the present invention caneffectively solve the problem of eliminating formaldehyde contained inthe product system, and meanwhile does not affect other requiredproducts in the system, with very high selectivity and efficiency ofcatalyst.

Comparative Example 1

This comparative example is based on the same equilibrium system ofproducts containing polyoxymethylene dimethyl ethers as in Embodiment 1,but the refining step as in Embodiment 1 is omitted, instead the overallequilibrium system after synthesis directly enters the extraction unit,and Comparative Example 1 utilizes the same extraction means as inEmbodiment 1 to extract the products with various degrees ofpolymerization. After the extraction is finished, the testing result ofextraction rate of the products is shown in Table 3.

TABLE 3 extraction rate of the products Constituents FormaldehydeContent of content after Recovery ratio ΣPODE₂₋₈ in atmospheric of thetarget Purity of the the equilibrium rectification/ product targetproduct Number products/wt % wt % ΣPODE₂₋₈/% ΣPODE₂₋₈/% Embodiment 154.0 0.01 ~100 99.9 Comparative example 1 54.0 7.4 ~32.0 ~92.6

The equilibrium systems of products containing polyoxymethylene dialkylethers in Embodiment 3-1 to Embodiment 6-2 of the present invention arethe same, the preparation method of which is that:

In a 2 L pressurized slurry bed reactor, 60˜80 g strongly acidiccatalyst of Amberlyst15 cation exchange resin is added, and then 1200 gin total of paraformaldehyde (or trioxane) and ethanol (or propanol,butanol, pentanol) at various molar ratios are added, wherein the molarratios are within 1:1˜2:1. First the air in the reactor is replaced bynitrogen, then 1.5 MPa of initial nitrogen is filled in. The reactionmixture is heated up to the reaction temperature of 70-130° C. andreacts under stirring for 0.5˜6 hours, thereby the equilibrium systemsof products respectively containing polyoxymethylene diethyl ether,polyoxymethylene dipropyl ether, polyoxymethylene dibutyl ether andpolyoxymethylene dipentyl ether are obtained.

Embodiment 3-1

First, 63 g Raney-Cu catalyst is loaded into a 2 L pressurized slurrybed reactor of refining by hydrogenation;

Then, an equilibrium system of 1260 g products containingpolyoxymethylene diethyl ethers is refined by catalytic hydrogenation,the amount of Raney-Cu catalyst used is equal to 5 wt % of the overallreaction products to be refined, and the process conditions are: thehydrogen pressure is 3 Mpa, the reaction temperature of refining by theslurry bed (i.e. the reaction temperature of catalytic hydrogenation) is100° C., and the reaction time is 5 hours;

Finally, the formaldehyde contained is hydrogenated into methanol by thecatalytic function of Raney-Cu, and the methanol generated constitutes acomponent of the equilibrium products, thereby no other foreigncomponent is generated while removing formaldehyde. The constituents anddistribution of the main products before and after refining by catalytichydrogenation are shown in Table 4-1.

The equilibrium system after refining is extracted, and the extractionprocess utilizes the atmospheric rectification technology, with towerplate number of 20˜50, gas temperature of 45˜65.0° C. at tower top,temperature of 110˜130° C. at tower bottom, feedstock temperature of60˜90° C., and reflux ratio of 1.0˜3.0. After the extraction isfinished, the testing result of extraction rate of the products is shownin Table 4-2.

TABLE 4-1 constituents and distribution of the main products before andafter refining by hydrogenation catalyzed by Raney-Cu catalystConstituents Conversion Ethanol Formaldehyde Methanol PODE₁ ΣPODE₂₋₆rate of Selectivity System wt % wt % wt % wt % wt % formaldehyde/% ofcatalyst/% Before refining 5.1 4.7 0 38.0 52.2 — — by hydrogenationAfter refining 5.1 0.00 4.7 38.0 52.2 ~100 ~100 by hydrogenation

Embodiment 3-2

This embodiment is based on the same synthesis product system as inEmbodiment 3-1, but the refining step as in Embodiment 3-1 is omitted,instead the overall equilibrium system after synthesis directly entersthe extraction unit, and Embodiment 3-1 and Embodiment 3-2 utilize thesame extraction means to extract the products with various degrees ofpolymerization.

TABLE 4-2 extraction rate of the products Constituents FormaldehydeContent content after Recovery of ΣPODE₂₋₆ atmospheric ratio of thePurity of the in the equilibrium rectification/ target product targetproduct Number products/wt % wt % ΣPODE₂₋₆/% ΣPODE₂₋₆/% Embodiment 3-152.2 ~0.0 ~99.9 99.9 Embodiment 3-2 52.2 8.6 ~36.5 ~91.4

Embodiment 4-1

First, 88.2 g Raney-Ni catalyst is loaded into a 2 L pressurized slurrybed reactor of refining by hydrogenation;

Then, an equilibrium system of 1260 g products containingpolyoxymethylene diethyl ethers is refined by catalytic hydrogenation,the amount of Raney-Ni catalyst used is equal to 7 wt % of the overallreaction products to be refined, and the process conditions are: thehydrogen pressure is 4 Mpa, the reaction temperature of refining by theslurry bed (i.e. the reaction temperature of catalytic hydrogenation) is80° C., and the reaction time is 3.5 hours;

Finally, the formaldehyde contained is hydrogenated into methanol by thecatalytic function of Raney-Ni, and the methanol generated constitutes acomponent of the equilibrium products, thereby no other foreigncomponent is generated while removing formaldehyde. The constituents anddistribution of the main products before and after refining by catalytichydrogenation are shown in Table 5-1.

The equilibrium system after refining is extracted, and the extractionprocess utilizes the atmospheric rectification technology, with towerplate number of 20˜50, gas temperature of 45˜65.0° C. at tower top,temperature of 110˜130° C. at tower bottom, feedstock temperature of60˜90° C., and reflux ratio of 1.0˜3.0. After the extraction isfinished, the testing result of extraction rate of the products is shownin Table 5-2.

TABLE 5-1 constituents and distribution of the main products before andafter refining by hydrogenation catalyzed by Raney-Ni catalystConstituents Conversion Propanol Formaldehyde Methanol PODE₁ ΣPODE₂₋₆rate of Selectivity System wt % wt % wt % wt % wt % formaldehyde/% ofcatalyst/% Before refining 4.5 3.8 0 31.6 60.1 — — by hydrogenationAfter refining 4.5 0.01 3.8 31.6 60.1 ~99.7 ~100 by hydrogenation

Embodiment 4-2

This embodiment is based on the same synthesis product system as inEmbodiment 4-1, but the refining step as in Embodiment 4-1 is omitted,instead the overall equilibrium system after synthesis directly entersthe extraction unit, and Embodiment 4-1 and Embodiment 4-2 utilize thesame extraction means to extract the products with various degrees ofpolymerization.

TABLE 5-2 extraction rate of the products Constituents FormaldehydeContent of content after Recovery ratio ΣPODE₂₋₆ in the atmospheric ofthe target Purity of the equilibrium rectification/ product targetproduct Number products/wt % wt % ΣPODE₂₋₆/% ΣPODE₂₋₆/% Embodiment 4-160.1 0.01 99.9 99.8 Embodiment 4-2 60.1 9.3 ~46.0 ~90.7

Embodiment 5-1

First, 50.4 g Raney-Cu catalyst is loaded into a 2 L pressurized slurrybed reactor of refining by hydrogenation;

Then, an equilibrium system of 1260 g products containingpolyoxymethylene diethyl ethers is refined by catalytic hydrogenation,the amount of Raney-Cu catalyst used is equal to 4 wt % of the overallreaction products to be refined, and the process conditions are: thehydrogen pressure is 4 Mpa, the reaction temperature of refining by theslurry bed (i.e. the reaction temperature of catalytic hydrogenation) is100° C., and the reaction time is 4 hours;

Finally, the formaldehyde contained is hydrogenated into methanol by thecatalytic function of Raney-Cu, and the methanol generated constitutes acomponent of the equilibrium products, thereby no other foreigncomponent is generated while removing formaldehyde. The constituents anddistribution of the main products before and after refining by catalytichydrogenation are shown in Table 6-1.

The equilibrium system after refining is extracted, and the extractionprocess utilizes the atmospheric rectification technology, with towerplate number of 20˜50, gas temperature of 45˜65.0° C. at tower top,temperature of 110˜130° C. at tower bottom, feedstock temperature of60˜90° C., and reflux ratio of 1.0˜3.0. After the extraction isfinished, the testing result of extraction rate of the products is shownin Table 6-2.

TABLE 6-1 constituents and distribution of the main products before andafter refining by hydrogenation catalyzed by Raney-Cu catalystConstituents Conversion Butanol Formaldehyde Methanol PODE₁ ΣPODE₂₋₆rate of Selectivity System wt % wt % wt % wt % wt % formaldehyde/% ofcatalyst/% Before refining 11.3 4.5 0 27.6 56.6 — — by hydrogenationAfter refining 11.3 0.00 4.5 27.6 56.6 ~100 ~100 by hydrogenation

Embodiment 5-2

This embodiment is based on the same synthesis product system as inEmbodiment 5-1, but the refining step as in Embodiment 5-1 is omitted,instead the overall equilibrium system after synthesis directly entersthe extraction unit, and Embodiment 5-1 and Embodiment 5-2 utilize thesame extraction means to extract the products with various degrees ofpolymerization.

TABLE 6-2 extraction rate of the products Constituents FormaldehydeContent of content after Recovery ratio ΣPODE₂₋₆ in the atmospheric ofthe target Purity of the equilibrium rectification/ product targetproduct Number products/wt % wt % ΣPODE₂₋₆/% ΣPODE₂₋₆/% Embodiment 5-156.6 0.01 ~99.9 99.8 Embodiment 5-2 56.6 7.8 ~48.5 ~92.2

Embodiment 6-1

First, 37.8 g Raney-Ni catalyst is loaded into a 2 L pressurized slurrybed reactor of refining by hydrogenation;

Then, an equilibrium system of 1260 g products containingpolyoxymethylene diethyl ethers is refined by catalytic hydrogenation,the amount of Raney-Ni catalyst used is equal to 3 wt % of the overallreaction products to be refined, and the process conditions are: thehydrogen pressure is 4 Mpa, the reaction temperature of refining by theslurry bed (i.e. the reaction temperature of catalytic hydrogenation) is90° C., and the reaction time is 4.5 hours;

Finally, the formaldehyde contained is hydrogenated into methanol by thecatalytic function of Raney-Ni, and the methanol generated constitutes acomponent of the equilibrium products, thereby no other foreigncomponent is generated while removing formaldehyde. The constituents anddistribution of the main products before and after refining by catalytichydrogenation are shown in Table 7-1.

The equilibrium system after refining is extracted, and the extractionprocess utilizes the atmospheric rectification technology, with towerplate number of 20˜50, gas temperature of 45˜65.0° C. at tower top,temperature of 110˜130° C. at tower bottom, feedstock temperature of60˜90° C., and reflux ratio of 1.0˜3.0. After the extraction isfinished, the testing result of extraction rate of the products is shownin Table 7-2.

TABLE 7-1 constituents and distribution of the main products before andafter refining by hydrogenation catalyzed by Raney-Ni catalystConstituents Conversion Pentanol Formaldehyde Methanol PODE₁ ΣPODE₂₋₆rate of Selectivity System wt % wt % wt % wt % wt % formaldehyde/% ofcatalyst/% Before refining 12.4 7.2 0 34.1 46.3 — — by hydrogenationAfter refining 12.4 0.00 7.19 34.1 46.3 ~99.8 ~100 by hydrogenation

Embodiment 6-2

This embodiment is based on the same synthesis product system as inEmbodiment 6-1, but the refining step as in Embodiment 6-1 is omitted,instead the overall equilibrium system after synthesis directly entersthe extraction unit, and Embodiment 6-1 and Embodiment 6-2 utilize thesame extraction means to extract the products with various degrees ofpolymerization.

TABLE 7-2 extraction rate of the products Constituents FormaldehydeContent of content after Recovery ΣPODE₂₋₆ in the atmospheric ratio ofthe Purity of the equilibrium rectification/ target product targetproduct Number products/wt % wt % ΣPODE₂₋₆/% ΣPODE₂₋₆/% Embodiment 6-146.3 0.02 99.9 99.8 Embodiment 6-2 46.3 6.2 ~39.5 ~93.8

It can be seen from the data of extraction in the foregoing embodimentsthat, in the equilibrium system obtained by the synthesis unit, if theformaldehyde contained is not specifically removed, then no matter howideal the product distribution of the synthesis part is, it is alwaysunable to obtain satisfactory products. However, the system that hasbeen through the refining process by hydrogenation of the presentinvention only requires simple ordinary extraction operations to achieveextraction of products with various degrees of polymerization and toobtain the effects of satisfactory product yield and product purity.Therefore, as a step of the entire production process, the refining unitplays a crucial role in obtaining of the target products. Moreimportantly, the technological process of the present invention forrefining by catalytic hydrogenation using a slurry bed achieves an atomutilization ratio close to 100%, does not discharge any waste water orwaste residue during the entire process, not only has satisfactoryextraction results, but also is green and environmental as a whole,which has great practical significance.

Obviously, the aforementioned embodiments are merely intended forclearly describing the examples, rather than limiting the implementationscope of the invention. For those skilled in the art, various changesand modifications in other different forms can be made on the basis ofthe aforementioned description. It is unnecessary and impossible toexhaustively list all the implementation ways herein. However, anyobvious changes or modifications derived from the aforementioneddescription are intended to be embraced within the protection scope ofthe present invention.

1. A method for refining polyoxymethylene dialkyl ethers by catalytichydrogenation using a slurry bed, characterized in that, using a slurrybed reactor and in the presence of catalyst, an equilibrium system ofproducts containing polyoxymethylene dialkyl ethers is refined bycatalytic hydrogenation, so as to remove formaldehyde contained therein,and subsequent extracting operations are performed on the products afterformaldehyde removal.
 2. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 1, characterized in that, said catalyst isskeletal metal catalyst.
 3. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 2, characterized in that, said catalyst isRaney-Co, Raney-Fe, Raney-Ru, Raney-Ni catalyst, Raney-Cu catalyst orcombinations thereof.
 4. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 3, characterized in that, the amount of saidRaney-Ni catalyst used is equal to 0.2-10 wt % of said products to berefined by hydrogenation.
 5. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 4, characterized in that, the amount of saidRaney-Ni catalyst used is equal to 3-8 wt % of said products to berefined by hydrogenation.
 6. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 3, characterized in that, the amount of saidRaney-Cu catalyst used is equal to 0.2-10 wt % of said products to berefined by hydrogenation.
 7. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 6, characterized in that, the amount of saidRaney-Cu catalyst used is equal to 3-8 wt % of said products to berefined by hydrogenation.
 8. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 1, characterized in that, the amount offormaldehyde contained in said equilibrium system of products containingpolyoxymethylene dialkyl ethers is 0.5-20 wt %.
 9. The method forrefining polyoxymethylene dialkyl ethers by catalytic hydrogenationusing a slurry bed in accordance with claim 8, characterized in that,the process conditions of said refining by catalytic hydrogenation arethat: the hydrogen pressure is 1-10 Mpa, the reaction temperature ofcatalytic hydrogenation is 60-150° C., and the reaction time is 2-8hours.
 10. The method for refining polyoxymethylene dialkyl ethers bycatalytic hydrogenation using a slurry bed in accordance with claim 9,characterized in that, the process conditions of said refining bycatalytic hydrogenation are that: the hydrogen pressure is 2-6 Mpa, thereaction temperature of catalytic hydrogenation is 70-120° C., and thereaction time is 3-6 hours.
 11. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 1, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 12. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 2, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 13. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 3, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 14. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 4, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 15. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 5, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 16. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 6, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 17. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 7, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 18. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 8, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 19. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 9, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.
 20. The method for refining polyoxymethylenedialkyl ethers by catalytic hydrogenation using a slurry bed inaccordance with claim 10, characterized in that, said extracting stepcomprises one or more operations selected from atmospheric distillation,reduced pressure distillation, flash evaporation, rectification, phaseseparation and filtration.